Boring is defined as a technology for boring a deep hole in the ground. In order to conduct extracting oil or natural gas, developing geothermal energy or hot springs and ventilation, drainage of water, pumping water, blasting, etc., in addition to a close examination of the earth's crust, such as geological structure of the underground, distribution of rock types, or probes for mineral deposit, the boring is performed. Boring holes of various diameters and various depths may be formed; the boring method by various boring devices may be classified into an impact-type boring and a rotary-type boring.
The impact-type, in that a hole is developed by making a bit suspended to the end of the wire rope at the predetermined height free fall, impacting the bottom of the hole, and crushing the ground, thereby developing the hole vertically into the ground, may be used in relatively shallow boring within hundreds meters depth. The first drilling machine of the impact-type is one invented in 1803 by I. M. Singer of the United States of America. The rotary-type boring, widely used, may bore a hole in any direction. The rotary-type boring may be performed by elongating a steel pipe, called a drilling pipe in a proper length, pressing and rotating a bit fixed to the end of the steel pipe toward the bottom of a hole, and cutting the ground, and the boring hole has reached to 8,000 m in an oil land in U.S.A. The first steam boring machine of this type has been invented around 10 by an English mechanical engineer, called as Trevithick, R. A bit used in the rotary boring, may be selected from a metal bit, a rock bit and a diamond bit according to the hardness of the ground to be bored. A metal bit has an end of ultra hard metal cemented carbide, and a rock bit used in hard rock is comprised of several cone-type rollers having a plurality of protrusions, which crushes rock by wedge functions of the protrusions when rotating over the bottom surface of the hole. As a diamond bit used in hard rock or ultra hard rock, there are one inserted with diamond particles in the end of the blade, and the other having the blade made of mixture of fine diamonds and metal powder sintered under vacuum atmosphere. Both borings use abrasion effect of rock by diamond particles, are called a diamond boring, a boring using a diamond bit
Core bits which form circular ring in the earth and leave a core in the center, are widely used in the rotary boring for geological examination. The core, a sample ore of base rock, is used in the close examination for composition or properties of rock. This is called as a core boring. A container, a core tube installed between the core bit and a drilling tube, preserves safety of the core. In the rotary boring, muddy water is injected into the hole though the drilling tube, being sprayed from the end of the bit and then being circulated for cooling the end of the blade, discharging bored dregs and protecting the wall of the hole. In boring the ground having weak layers or layers having gushing water, a casing pipe, a thin steel pipe protects the hole. There is a short ball boring, in which the boring is performed by mixing short balls of small grain in the muddy water, and colliding together, thereby crushing rock. Recently, a tunnel digging machine and a pit excavation machine, as an application of large hole boring, are developed. In particular, a boring is required for strengthening the ground in a tunnel construction, in a building construction such as an apartment, in a structure construction such as a subway, or for forming a wall for blocking soil or water.
Meanwhile, the grounds for being bored or drilled are largely classified into soil layers that have soil and sands and are easily bored, and rock layers that are hard to be bored. And the general grounds include soil layers and rock layers, and the rock layers may curve the boring path when boring.
In other words, in case of the ground including rock layers, soil layers make no deviation in the boring path, but rock layers may make any deviation in the designed boring path due to the hardness of the rock layers.
In particular, this may require an additional working for filling a gap formed between the adjacent piles in order to stopping water leaks in the underground.